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Author Topic: Which is more reactive with sodium hydroxide  (Read 1863 times)

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born2dive00

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Re: Which is more reactive with sodium hydroxide
« Reply #15 on: January 01, 2019, 01:04:55 AM »

Hello Borek and happy new year

The phosphoric acid is 85% food grade, and believe it or not readily avaiable in cairo for some strange reason.

i think i am understanding this, so if i have Say 4567.48mg mg of tri sodium phosphate, which is a base salt, this will use up all 1921.527919 mg of  sodium in the solution, and but only 862.9489497 of the 2177.731641mg of phosphorus, that means i have to add 2.897 ml of 85% phosphoric acid to make up the missing phosphorus. this u
would bring the pH near (my guess) from around pH 17 to some where around the 6-8pH mark. this i understand and i understand also that things would start dissassociate here so the phosphoric acid that was not associated with the TSP would start forming new sodium phosphopate's

now that we have all the phosphorus and the sodium accounted for, i add the caffeine, which should form caffeine phosphate, caffeine phosphate has a ph of 6.8-7.1 so this should not have much effect on the over all pH and probally will consume some if not all the free phosphoric acid. and wont have  major impact on the ph per se.

now as i understand it as i add more and more citric acid to the solution to bring up the final ph to 3 this will further cause dissassociation of the sodium on the phosphate to form sodium citrates.

and if i am not mistaken the phosphorus will dissacoiate from the caffeine and the citric acid (being the stronger of the 2 at a pH of 3 will now form caffeine citrate.

Borek now IF i understand you correctly what you are saying, it does not matter if i started out by adding the ingredients as described above, to the solution,  or if i started by using the tri sodium citrate first then the phosphorusic acid, adjusting the pH with the citric acid, the results will be the same at the pH of 3

is this correct?


i guess what i am trying to say is no matter which way the ingredients are added, once the 3 ph is achieved, the end results should be the same correct?

 




the amount of phosphoric acid  4.799 ml

Pure? Solution? What concentration?

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What i am not sure or is whether or not the citric acid is augmenting the pH or if it would be the Phosphoric acid that is changing the pH in this

In a way - both. As I signaled earlier as long as you put the same amount of basic components the equilibrium composition of the solution will be the same. For example you can mix:
  • 1 mole of citric acid, 1 mole of phosphoric acid and 3 moles of NaOH
  • 1 mole of trisodium citrate and 1 mole of phosphoric acid
  • 1 mole of citric acid and 1 mole of trisodium phosphate
  • 1 mole of disodium citrate and 1 mole of monosodium phosphate
and many other combinations - and the final solution will be identical. You can't assign the final pH to action of any single acid, it is result of their interactions.

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what he can not confirm is the amounts of the complex compounds that are formed once added to the soft drink, i.e. phosphoric acid + sodium hydroxide which forms mono, di, or tri sodium phosphate depending on the pH.

Equilibrium values can be calculated in a way I explained earlier.

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if i understand you correctly in what you say, in this formula it does not matter if the sodium compounds are of citrate or of phosphate, they will adjust by them selves. so for example if i use di sodium all of the sodium is used but i have excess of phosphorus if i use mono sodium phosphate i use up all the phosphosphorus but have excessive amount of sodium.

now if i add citric acid, the excess sodium /hydroxide will react with the citric acid to form sodium citrate

No, it doesn't work this way. Acids are not neutralized to the end before others start to react, they react at the same time to the extent determined by their pKa values.

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i am trying to figure out exactly how much di sodium phosphate i need to add,
how much phosphoric acid i need,
how much sodium citrate i need
how much caffeine citrate is needed
how much citric acid i need

You wrote you can't buy nor transport NaOH, but you list phosphoric acid - which is a highly corrosive liquid. I doubt you will be able to buy (and fly) concentrated food grade phosphoric acid, but the citric acid - which is a crystalline solid - shouldn't be difficult to find.
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born2dive00

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Re: Which is more reactive with sodium hydroxide
« Reply #16 on: January 01, 2019, 06:47:31 AM »

sorry pH of 12 with the tri sodium phosphate, brought down to near 7 id guess with the additional missing phosphoric acid.
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